1. Field of Invention
The embodiments of the invention generally relate to a ceramic support for supporting a substrate in a process chamber.
2. Background of the Invention
Substrate support chucks are widely used to support substrates within semiconductor processing systems. A particular type of chuck used in semiconductor processing systems, such as etch systems among other processing systems, is a ceramic electrostatic chuck. Electrostatic chucks generally retain a substrate or other workpiece in a stationary position during processing. Typically, electrostatic chucks contain one or more embedded electrodes within a ceramic body. As an electrical potential is applied between the electrodes and a substrate disposed on the ceramic body, an electrostatic attraction is generated which holds the substrate against a support surface of the ceramic body. The force generated may be a capacitive effect due to a potential difference between the substrate and the electrodes or, in the case of ceramic bodies comprised of semiconducting materials having a relatively low resistivity which allow charge migration within the ceramic body to the surface approximate the substrate, a Johnsen-Rahbeck effect. Electrostatic chucks utilizing capacitive and Johnsen-Rahbeck attractive forces are commercially available from a number of sources.
Typically, to control the substrate temperature during processing, a backside gas is provided between the support surface of the ceramic body and the substrate. Generally, the backside gas fills the interstitial area between the ceramic body and the substrate, thus providing a heat transfer medium that enhances the rate of heat transfer between the substrate and the substrate support.
The operation and service life of the electrostatic chuck may be adversely affected if backside gas becomes ignited into a plasma or facilitates arcing between the substrate and the substrate support. Arcing or the creation of plasma between the substrate and the wafer may damage both the substrate and the support surface of the electrostatic chuck. In particular, backside gas outlets disposed in the support surface are vulnerable to erosion or damage due to the concentration of gas flowing therethrough which provides a less resistive current path than the surrounding gas in the interstitial area.
One configuration of an electrostatic chuck that substantially reduces arcing and plasma discharge around the backside gas outlets disposed in the support surface includes a porous dielectric plug inserted in the outlet. The porous material blocks the direct electrical path between the backside of the substrate and the interior portions of the backside gas channel which are closer to the embedded conductive member (e.g., the electrodes). Moreover, the porous flow path provides less surface area surrounding the individual backside gas flows through the plug resulting in less charge accumulation proximate the gas flow. As less charge accumulation results in a lower potential at the outlets, arcing and gas ignition are substantially eliminated. Thus, the backside gas may flow to interstitial space between the substrate and the support surface through the porous material substantially without risk of damage to the chuck and/or substrate.
While the porous material provides good protection against plasma ignition and arcing at the backside gas outlets, fabrication of such chucks is difficult. For example, the porous plugs are typically inserted into a counterbore provided in the support surface and concentric with the backside gas outlet and retained therein using an adhesive. As a plurality of backside gas outlets are typically disposed in one electrostatic chuck, the fabrication steps of applying adhesive and inserting the plugs into the electrostatic chuck is timeconsuming and expensive. Moreover, such chucks having an adhesive bond exposed to the support surface risk chamber contamination during various portions of the processing cycle, particularly during plasma dry cleaning. During plasma dry cleaning, the portions of the adhesive exposed to the plasma may be removed from the plug to ceramic body joint and deposited elsewhere in the chamber, thereby becoming a potential substrate contamination source. Additionally, after a number of cleanings, the plug may become loose and eventually become disengaged from the chuck. Loose plugs are a source of unwanted particle contamination and may also come in contact with the substrate thus damaging the substrate.
Other electrostatic chucks utilizing porous plugs include a dielectric layer deposited over the chuck body after the porous inserts have been deposited in the outlet passages. In order to complete the backside gas flow path to the interstitial area after the deposition of the dielectric material, a passage must be fabricated in the dielectric coupling the plug to the surface of the dielectric material.
Although chucks configured in this manner are more conducive to plasma cleaning, fabrication and other concerns exist. For example, the fabrication of the electrostatic chuck now includes both a subsequent dielectric deposition and machining step. As the plugs are typically inserted without the use of adhesives, inconsistencies between the height of the porous plug and the support surface may result in variations in the topography of the applied dielectric layer. Moreover, if the plug moves away from the applied dielectric layer leaving a gap, gas within the gap is susceptible to plasma ignition. Furthermore, if the plug is loose and moves within the electrostatic chuck, particle generation may occur. Thus, the high fabrication costs along with the remaining possibility of plasma ignition within the passages utilized by the backside gas and the difficulty of maintaining a flat support surface leaves room for improvement in electrostatic chuck design.
Therefore, there is a need for an improved electrostatic chuck along with methods for fabricating the same.
One aspect of the invention generally provides a ceramic substrate support for supporting a substrate. In one embodiment, a ceramic substrate support includes a ceramic body and a porous member disposed therein. The ceramic body generally has an upper portion and a lower portion. The upper portion includes a support surface while the lower portion includes a bottom surface. At least one passage is disposed in the lower portion of the ceramic body. A first end of the passage is at least partially closed by a portion of the upper portion of the ceramic body. At least one outlet is disposed through the portion of the upper portion of the ceramic body closing the passage and fluidly couples the passage to the support surface.
In another embodiment, a ceramic substrate support for supporting a substrate includes a ceramic body having one or more conductive members and a porous ceramic member disposed therein. The ceramic body has an upper portion having a support surface and a lower portion having a bottom surface. At least one passage is disposed in the lower portion of the ceramic body. A first end of the passage is at least partially closed by the upper portion. At least one outlet is disposed through the upper portion of the ceramic body and fluidly couples the passage to the support surface. The porous ceramic member is disposed within the passage and sintered and processed to become a single member with the ceramic body.
In another aspect of the invention, a process chamber for processing a substrate includes an evacuable chamber having an interior volume having a gas supply fluidly coupled thereto and an electrostatic chuck disposed in the interior volume. The electrostatic chuck includes a ceramic body having one or more conductive members and a porous member disposed therein. The ceramic body has an upper portion having a support surface and a lower portion having a bottom surface. At least one passage is disposed in the lower portion of the ceramic body. A first end of the passage is at least partially closed by the upper portion. At least one outlet is disposed through the upper portion of the ceramic body and fluidly couples the passage to the support surface.
In another aspect of the invention, a method for fabricating a ceramic substrate support is provided. In one embodiment, a method for fabricating a ceramic substrate support includes the steps of forming one or more blind holes on a first side of a first ceramic member, inserting a porous ceramic member in each blind hole, disposing a second ceramic member on the first side of the first ceramic member and processing the first ceramic member, second ceramic member and porous ceramic member to form a single ceramic body.
In another embodiment, a method for fabricating a ceramic substrate support pedestal includes forming one or more blind holes in a first side of a first ceramic member having a resistivity between 1xc3x97E9 to about 1xc3x97E11 ohms-cm, inserting a porous ceramic member in each of the blind holes, disposing a second ceramic member having a resistivity higher than the first ceramic member on the first side of the first ceramic member, disposing one or more electrodes between the first ceramic member and the second ceramic member, processing the first ceramic member, the second ceramic member and the porous ceramic member to form a single ceramic body and forming one or more outlets in the first ceramic member to couple each blind hole to a second side of the first ceramic member.